Passive ranging system

Abstract

A passive distance measuring system for aircraft landing or other transportation related or other general usage is disclosed. The passive system operates by measuring the time interval between arrival of a precision sweep scanned signal such as a radio frequency signal at two widely dispersed different signal receptor locations on the aircraft. By knowing the angular sweep velocity of the received signals and the receptor or antenna separation distance on the aircraft, the distance of the aircraft from the scanning source of, for example, radio frequency signals may be computed with appreciable precision. The disclosure includes analog-to-digital signal conversion and modifications of the invention including optical or laser signals in lieu of the preferred microwave radio frequency signals. The disclosure also includes a table of numeric values relating pulse separation time to aircraft range distance and indicates a number of equipment and military environment advantages of the invention.

I claim: 
     
       1. Aircraft ranging apparatus comprising: source means located at a radius vector terminal point for generating a narrow beam of microwave radio frequency energy having a fixed predetermined angular sweep velocity about said radius vector terminal point;   said source means including an aircraft microwave landing system radio frequency energy source having electronically scanned antenna array means for accomplishing remote craft azimuth guidance;   said narrow beam of microwave radio frequency energy also having a scanning velocity, along a cord vector perpendicular to said radius vector, that is proportional to a said aircraft range determined length of said radius vector;   means for measuring a delay time interval between arrival of said source means originated microwave radio frequency energy signals at predetermined physical distance segregated radio frequency antennas located at opposed wingtip extremities points contiguous of said aircraft; and   means for computing from said aircraft predetermined physical segregation distance, said fixed predetermined angular sweep velocity, and said measured delay time interval, a radius vector length range of said aircraft from said terminal point radio frequency energy source.   
     
     
       2. The apparatus of claim 1 wherein said antenna array means has a scanning rate angular velocity of twenty thousand degrees per second. 
     
     
       3. The apparatus of claim 1 wherein said means for computing further includes means for correcting said computed radius vector length range for aircraft roll and yaw angles differing from level flight along a radius vector aligned with said terminal point. 
     
     
       4. The apparatus of claim 1 wherein said means for measuring includes signal processing means for identifying corresponding envelope waveform points on radio frequency envelope waveform signals received from said source means via said aircraft physical distance segregated points. 
     
     
       5. The apparatus of claim 4 wherein said means for identifying corresponding envelope waveform points comprises one of the signal processing techniques taken from the group comprised of: a cross correlation mathematical function;   a frequency domain Fourier transform mathematical algorithm;   a time domain Fourier transform mathematical algorithm;   a Fast Fourier Transform mathematical algorithm;   a waveform peak detector; and   an analog-to-digital converter.   
     
     
       6. The apparatus of claim 1 wherein said microwave landing system includes a radio frequency beamwidth smaller than two degrees of azimuth and includes a beam sweep angle of sixty degrees. 
     
     
       7. The apparatus of claim 1 wherein said microwave landing system includes a "TO" sweep comprising beam movement in one of a clockwise and counterclockwise sweep direction and a "FRO" sweep comprising beam movement in the opposite of said clockwise and counterclockwise sweep directions and wherein said apparatus further includes signal processing means for increasing the accuracy of said radius vector length computation by averaging signals generated during said "TO" and "FRO" direction sweeps. 
     
     
       8. The method for determining aircraft range from a measuring location comprising the steps of: disposing a narrow beam source of radio frequency energy of predetermined azimuth angular sweep velocity at a center point of an azimuth circle located at said measuring location;   said azimuth circle also including a radially oriented range vector originating at said center point and extending to said aircraft;   measuring a sweep angular velocity related time interval between arrival of said narrow beam energy at two azimuth circle cord elements defining physically separated opposed wingtip points on said aircraft; and   computing from said predetermined angular sweep velocity, said measured time interval, and said cord element aligned wingtip physical separation distance, a range distance along said radial vector, between said azimuth circle center point located source of radio frequency energy and said aircraft;   said computing step including correction for one of the conditions of said aircraft's wings being in a roll angle position with respect to a horizon reference and said aircraft being disposed in a yaw angle orientation with respect to said range vector.   
     
     
       9. The method of claim 8 wherein said narrow beam source of radio frequency energy comprises a microwave energy source having landing assistance capability and a predetermined range of electronic scanning generated angular displacement within said azimuth circle. 
     
     
       10. Aircraft distance to runway measuring apparatus of a passive non radiating type comprising the combination of: ground based Microwave Landing System apparatus of microwave "C" band operating frequency, a radiated radio frequency energy output beam of twenty thousand degrees per second sweep rate, sweep extending over a total angle of sixty degrees of azimuth on either side of a runway centerline, and a beam width not exceeding three degrees of azimuth;   radio frequency receiver means including first and second receiving antenna members of predetermined physical separation distance disposed at opposite wingtip locations of said aircraft;   said receiver means also including signal processing means for identifying predetermined radio frequency carrier envelope waveform locations on said received radio frequency signals;   said receiver means also including electrical circuit means for measuring a time interval between sweeping of said output beam between said first and second receiving antenna members on said aircraft in response to said predetermined fixed azimuthal sweep rate and means for relating said measured time interval to a distance measurement between said aircraft and said runway;   said receiver means also including signal processing means for correcting a computed range distance for non zero angles of roll and yaw of said aircraft.